1. Field of the Invention
The invention relates to a method for producing a single crystal of semiconductor material, in which semiconductor material granules are melted on a dish that has a run-off tube consisting of the semiconductor material, and a melt of molten granules is formed, which extends from the run-off tube in the form of a melt neck and a melt waist to a phase boundary, and heat is delivered to the melt by means of an induction heating coil which has an opening through which the melt neck passes, and the melt is crystallized at the phase boundary.
2. Background Art
Such a method is described, for example, in US 2003145781 A. It makes it possible to produce a single crystal of semiconductor material with granules as raw material. FIG. 4 of US 2003145781 A shows a device which is suitable for carrying out the method. The granules are melted on a dish, in the middle of which there is a passage opening extended to a run-off tube. A first induction heating coil, arranged above the dish, is used to melt the granules. The molten granules form initially a film, and in the further course of the method, a melt which crystallizes at a phase boundary and thereby increases the volume of the growing single crystal. The crystallizing volume is compensated for by a corresponding volume of newly melted granules. The melt extends from the run-off tube to the phase boundary, at which the single crystal grows. In the region of the run-off tube, it has the form of a melt neck which passes through the opening of a second induction heating coil and merges into a wider melt waist, which lies on the growing single crystal. With the aid of the second induction heating coil, heat is delivered to the melt in order to control the growth of the single crystal.
Since the run-off tube consists of the semiconductor material, it may be caused to melt by the second induction heating coil if the energy input is correspondingly high. On the other hand, the run-off tube may grow downward if the energy provided by the second induction heating coil is not sufficient to keep the melt liquid in the region of the run-off tube. The position of the interface between the run-off tube and the melt must not however be displaced arbitrarily far axially, i.e. upward or downward. If the interface migrates too far upward because the run-off tube is melted, the volume of the melt neck increases and the risk arises that the melt will touch the second induction heating coil or the melt neck will become too thin and break. If the interface migrates too far downward because the run-off tube grows in this direction, the risk arises that the run-off tube will freeze up and block the melt flow. These two situations must not occur, because they prevent further growth of the single crystal.